Question

Which of the following textures suggest(s) post-kinematic growth of the mentioned mineral?

• A. Randomly oriented chlorite grain aggregates pseudomorphing porphyroblast
• B. Garnet porphyroblast wrapped by external foliation
• C. Foliation defining biotite wrapping around a porphyroblast
• D. Porphyroblastic garnet containing helictic fold as internal schistosity

Hint:

Post-kinematic porphyroblasts show foliation bending or wrapping around them. In contrast, syn-kinematic porphyroblasts preserve internal inclusion trails aligned with or oblique to the external foliation.

Answer 1

The Correct Option is B, C

Step 1: Post-kinematic growth definition.
Post-kinematic growth occurs when a mineral crystallizes after deformation has ceased. In such cases, foliation or external structures wrap around the porphyroblast, rather than being included inside it.

Step 2: Check each option.
- (A) Random chlorite pseudomorphing a porphyroblast → replacement texture, not necessarily post-kinematic.
- (B) Garnet wrapped by external foliation → foliation formed after garnet crystallization stopped → indicates post-kinematic growth → Correct.
- (C) Foliation defining biotite wrapping around porphyroblast → again suggests porphyroblast formed before deformation ended, thus post-kinematic → Correct.
- (D) Garnet with helictic folds (inclusion trails) → indicates syn-kinematic growth, not post-kinematic.

Step 3: Conclusion.
Post-kinematic textures are best represented by (B) and (C).

Final Answer: \[ \boxed{\text{(B) and (C)}} \]